Noto Mamoru, the protagonist, has his mind set on finally getting into the university he wants. For that purpose he moves into the apartment that is owned and managed by his aunt, Ichido Haruno, where he studies for the entrance exams.
Up until that point, Mamoru never thought of Haruno as anyone other than his aunt.
And she only saw him as a nephew who had to pass his entrance exams.
This perfectly normal relationship starts to change with the introduction of a single woman.

[From DLsite]